Abstract

Studies of the detection of simple visual patterns at threshold contrast have found that human performance is limited by the addition of internal noise and by the sub-optimal sampling efficiency of the visual system. Many common visual tasks require the detection of a signal having a contrast well above threshold, and we sought to measure the internal noise and sampling efficiency for such signals using simple reaction time (RT). Observers were presented with suprathreshold Gabors in dynamic Gaussian white noise and were required to hit a button as soon as each was detected. By comparing the RT variances from humans to those of an ideal observer, visuomotor internal noise and sampling efficiency were measured. The internal noise remains constant and the sampling efficiency increases as the signal contrast increases.